1. Field of the Invention
The present invention relates to a system for clamping and drilling matching bolt holes in the skin and stringers of a wing structure to prevent the formation of interlaminate burrs from forming between the skin and stringers thereby significantly reducing processing time and effort.
2. Description of the Prior Art
The wing structures of certain types of relatively large commercial and military aircraft have a number of components that are joined together to form the finished wing. Such components include the two opposite skins, longitudinally extending stringers, and transversely extending ribs which are primary as well as numerous other components which are secondary in nature. It is common practice for the interior of the wing to serve as a fuel tank. As a result, it is imperative that the completed wing structure be fluid tight. Thus, it is impermissible for there to be a gap, for example, between a stringer and the skin of the wing such that leaks could occur through fastener holes. Efforts to prevent the formation of such gaps are continuous in the course of the assembly process and cause the construction of modern aircraft wings, especially for large commercial and military aircraft, to be a highly labor intensive activity.
In a typical procedure, the stringers for a panel of a wing or other airfoil structure are initially drilled with pilot holes, then mounted in a fixture or jig so as to assume precise relative positions. The jig includes a large number of contour boards which define the contour of the wing panel and also identify the location of each stringer. The stringers are then clamped to the contour boards at spaced locations along their length.
When the stringers have been properly located in the jig, the outer skin is moved into position against the stringers and properly located, again with aid of the contour boards. The skin, in turn, is clamped to the contour boards of the jig. An operator then drills through the pilot holes into the adjacent skin and attaches temporary fasteners in each location at which a pilot hole has been drilled through both the stringer and the skin. This same procedure is performed at all appropriate locations along the length of each stringer. Then, from the skin side, an operator first drills an undersize hole completely through both the skin and the stringer, then reams up to full size, then counter sinks the skin side for subsequent reception of a bolt which will be flush with the outer surface of the skin. Unfortunately, during this procedure, because the temporary jig clamps are placed at spaced locations along the length of each stringer, and not at the immediate location at which the drilling operation occurs, interlaminate burrs undesirably but consistently occur at the interface between the skin and the stringer creating a gap between the skin and the stringer. This gap is undesirable for the reasons stated above. Furthermore, if the resulting gap is not alleviated and a finished fastener is inserted through the drilled holes, it is common for the outer surface of the shank of the fastener to further extrude into the gap. This condition, if permitted to continue, also serves to substantially reduce the fatigue life of both the fastener and of the wing structure at that location. When it is considered that just one wing panel may require several hundred of these fasteners, the problem described becomes one of a first order of magnitude of concern.
While it is presently common for such interlaminate burrs to occur during the initial drilling operation, it is also common practice to require their elimination. In order to do this, it is, necessary to remove both the skin and the stringers from the jig and to deburr them at another location. When the deburring operation on both the skin and the stringers is completed, those components are again placed in the jig and suitably clamped. In customary fashion, a suitable sealant is applied to the mating surfaces to further assure a leak-proof assembly. After the stringers have been properly fastened to the skin, typically at each rib location, an automatic riveting machine is then operated to drill a large number of holes through the skin and stringer at closely spaced longitudinal locations and inserted and apply rivets at each of these locations.
The inventors are aware of a large number of machines and processes which are of value for the manufacturing efforts with which they are engaged. However, none of these known devices or methods have the ability to correct this interlaminate burr problem which has been described and which requires such labor intensive effort to correct.
Typical of the prior art known to the inventors is U.S. Pat. No. 4,601,618 to McEldowney which discloses a device utilized in the manufacture of aircraft structures which serves to locate a pilot hole that extends only part of the way through a workpiece. The device comprises a clamp which includes opposing jaws movable toward and away from each other along a movable axis. The jaws have aligned openings extending therethrough generally parallel to the operating axis. A pilot is provided which can project from one of the openings toward the opposing jaw and the jaws are biased together for clamping a workpiece between them. A drill bushing is provided in the other of the openings for guiding a drill bit for drilling the workpiece. The pilot can be subsequently removed from its associated opening to enable the pilot hole to be drilled all the way through the workpiece.
Another pertinent disclosure is provided in Patent No. 4,108,566 to Jones which discloses a mechanized contour-following drill machine for drilling and reaming holes in a contoured surface. The machine operates to orient a drill spindle of a drill assembly to a position perpendicular to a plane tangent to the contoured surface of a workpiece so that the centerline of the holes to be drilled are perpendicular to the contoured surface.
In Pat. No. 4,897,000 to Suzuki, apparatus is provided for counter sinking rivet holes preformed at circumferential spacings in the fuselage of an aircraft and in annular reinforcing ribs of H-shaped cross section in the fuselage at axial spacings. An operating cylinder has a piston rod to which is coupled an offset anvil for pressing the fuselage and a rib against a toolhead. An aligning pin is associated with the anvil for locating and engaging the preformed rivet holes. The countersink tool is operable when the fuselage and rib are firmly clamped. The piston rod and associated anvil are not only linearly displaceable but are also rotatable about their own axes by a fluid motor through an angle of at least 180.degree..
In Pat. No. 5,161,923 to Reccius, a drill machine is operated in combination with a clamping sleeve which is coaxial with the drill bit. The clamping sleeve coacts with a template to hold a pair of sheet workpieces together for the drilling operation.
While the prior art as exemplified by these patents relates to machines and processes which were significant when they were first developed and, indeed, still represent significant technology, none of them or any others known to the inventors possess the ability to correct the problem here addressed by the inventors.
It was in light, then, of the prior art as represented above, that the present invention has been conceived and is now reduced to practice.